1. Field of the Invention
The present invention relates to a process for recovering rare earth oxides from a waste rare earth phosphor.
2. Description of Prior Art
As red-emitting phosphors for CPT (Color Picture Tube) or CDT (Color Display Tube), rare earth phosphors such as Y.sub.2 O.sub.2 S:Eu, are widely employed. These phosphors contain expensive rare earth elements such as Y, Eu, Sm and Tb, as main components. Accordingly, they are comparatively expensive relative to the usual sulfide phosphors such as a blue-emitting phosphor ZnS:Ag or a green-emitting phosphor ZnS:Cu,Au,Al. During the preparation of these phosphors, it may happen that inferior products which do not meet the standard requirements are produced, or during the repeated use of such phosphors by mixing them with binders to form coating solutions for the production of cathode ray tubes, it may happen that impurities or foreign matters will be included to give inferior products. Heretofore, such rare earth phosphors failing to meet the standard requirements or phosphor coating solutions containing such inferior products (hereinafter referred to generally as "waste rare earth phosphors") used to be wasted. Namely, when the above-mentioned rare earth phosphors are employed for CPT or CDT, it is common to incorporate a very small amount of iron oxide (red iron oxide) as a red-pigment to improve the image quality, and it is common to use them together with a sulfide phosphor such as ZnS:Ag. Accordingly, waste rare earth phosphors not only are contaminated with impurities such as Fe, Zn, Ca or Al but also usually contain foreign matters such as metal fragments, inorganic pigments or organic substances. Up to the present there has been no economically feasible process for the recovery and purification of rare earth components from the waste rare earth phosphors.
As mentioned above, rare earth phosphors are expensive, and from the viewpoints of conservation of resources and economy, it is extremely advantageous to recover and reuse them as highly pure rare earth materials.